1. Field of the Invention
The present invention relates to medical optically active implants to treat blindness and method for implanting these implants into an animal including a human to allow detection of visible light by the blind or to repair damaged areas of the retina to allow the animal to retain visual acuity in the damages areas.
More particularly, the present invention relates to an implant including an array of optical microdetectors supported on or in a bio-absorbable substrate, where the microdetectors comprise a heterostructure. The present invention also relates to a method for making the implant, to a method for implanting the implant in an animal including a human and to methods for treating blindness, for replacing damaged retinal photo sensors and for ameliorating symptoms of diseases of the eye such as Retinitis Pigrnentosa (RP) and Age-related Macular degeneration (AMD).
2. Description of the Related Art
Recent efforts on external stimulation of retinal neuronal cells with electrical signals have resulted in visual brain sensation [1,3]. Several reports have established that stimulation of retinal neuronal cells with electrical signals can result in visual perception [2,15]. In view of this phenomenon, different approaches have been undertaken in order to restore the vision of a retinally blind person. This has been accomplished by either direct stimulation of the retina or direct retinal implant of an optical detector to stimulate retinal neuronal cells in a patient whose optical detectors are damaged [9,10,11,15]. Both epiretinal electrical stimulation [9,10] and retinal stimulation with implants placed in the subretinal space [11,15] have been investigated.
The implants can consist of an encapsulated micro-photodiode array with thousands of micro-contacts for localized electrical stimulation of the bipolar cells in the subretinal approach [11,15], or they can use external processing of visual information before it is sent to implanted electrodes in the epiretinal or subretinal space [9,10]. The latter systems utilize video cameras that capture the image and convert it to an electrical signal. The electrical signal is coded, then sent as telemetry to an implant receiver that decodes the signal and generates the desired current to stimulate retinal neurons.
By using a thin film optical device (TOD), it has been demonstrated that thin films of certain perovskite ferroelectric oxides show optical activities in the visible range of the electromagnetic spectrum [12]. These ceramic ferroelectric films are also shown to be stable in aqueous, basic or acidic solutions for long periods of time; while other photodetectors based on semiconductors require encapsulation and wire interconnects for integration into the eye.
Human photoreceptor topography studies indicate that the photoreceptors are in the shape of cones and rods, with different densities in different parts of the retina [4,5]. The photoreceptors are nominally hexagonally close-packed with receptor size varying between 2 to 5 microns.
Tissue or organ engineering develops functional devices such as microdetectors to substitute for the missing or malfunctioning tissues or organs in the human body. Bio-resorbable polymers that are fully degradable into the body's natural metabolites by simple hydrolysis under physiological conditions are the most desirable materials for the carrier of such functional substitutes in the human body.
Biodegradable polymers are well known as bio-materials for applications in cell transplantation and drug delivery [6,7]. In vitro dissolution of thin layers made from these polymers in simulated body fluid has been characterized in terms of film thickness, molecular weight and time of degradation [7,8]. Among these materials, poly (dl-lactic-co-glycolic acid) (PLGA) polymers have been widely utilized as a template for tissue and cell transplantation. This strategy is widely used and investigated for transplantation of many cells including retinal pigment epithelium (RPE). The disadvantage associated with these polymers is the time it takes to degrade which depends on the nature and, also, the thickness of the polymer.
Even though small microdetectors or other type of microdevices can be constructed using modern electronic fabrication techniques, the small size of such microdevices, which could approach the 5 micron size of human photo sensors, make the detector verifiably impossible to handle for individually implantation of such microdevices by current surgical techniques. Thus, surgical implantation is problematic for any micro-implantation of small devices, tissues or cell cultures.
Despite complex engineering issues, these different approaches for restoring vision in retinally blind people have led to encouraging preliminary results [2,15]. However, several questions need to be answered in order to better define the parameters influencing the optimal performance of such artificial retinas such as sensitivity, long-term stability, and the degree of spatial resolution that might be achieved by these devices. Moreover, the design of reliable and reasonably safe surgical procedures for implantation as well as biocompatibility and long term function of implanted devices still remain in the forefront of ongoing investigations.
The prior art is deficient in the lack of effective means of forming a surgically manipulable optical implant for replacement of damagee retinal photo sensor or for allowing the sightless to see. More specifically, the prior art is deficient in the lack of effective means for handling arrays of optical microdetector devices for implantation into the retina of the eye and for means of making suitable implants for implantation into the retina of an animal.
Thus, there is a need in the art for implants that can be handled using standard surgical techniques, for implants that include optical detectors distributed in a similar manner to the photoreceptors of an animal including a human eye and to methods for making such implants and implanting such implants.